Inlet Widening

Inlet Widening had been evaluated for Bournes Pond and Little Pond before the passage of Article 17. This analysis indicated that widening these two inlets could provide an immediate and cost-effective improvement in water quality, and reduce the amount of sewering required for traditional wastewater nitrogen management in this watershed. Concurrently, the CCWPC (a Barnstable County organization) had been working to streamline the permitting process for non-traditional wastewater and nitrogen management concepts, with a focus on inlet widening projects. Working with the Town of Falmouth, the CCWPC hired a consultant to prepare and file an Environmental Notification Form and Waiver for the Bournes Pond Inlet Opening in a project called the Bournes Pond Restoration and Improvement Project. The project proposed augmentation of the existing 50-foot bridge over the inlet with an additional 50-foot bridge. Little quantitative information was provided on the benefits and cost of such a project. The regulatory community raised many questions about the proposed project and the ENF was withdrawn.

After the passage of Article 17, the WQMC revisited this option and considered which inlet opening to study further. Bournes Pond was chosen based on the significant gains in tidal flushing and nitrogen-removal that seemed to be likely, as well as public support from residents in the Bournes Pond area. Moreover, neighbors in the Little Pond area opposed widening of the Little Pond inlet.

Widening Analysis

The Town of Falmouth has selected GHD Engineering Inc., and its subcontractor Applied Coastal Research and Engineering, Inc. to analyze the cost and benefits of inlet widening at Bournes Pond. This design includes environmental and economic assessments. The reduction in the concentration of nitrogen that inlet widening should achieve will also be quantified.

In late 2012, the Town's WQMC initiated the Bournes Pond Inlet Opening Demonstration Project to evaluate this option quantitatively and to obtain greater detail on the implications of such a project. A consultant team (GHD, Applied Coastal Research and Engineering, and BETA Group) was hired to determine optimal inlet opening size, alternative bridge types to maintain the opening, capital and O&M costs of the revised opening, nitrogen management benefits, the effective nitrogen removal that would be provided by the new inlet opening, and potential cost savings of the inlet opening as compared to removing the same amount of nitrogen through conventional wastewater nitrogen management methods.

Evaluations & Findings

The evaluations and findings are summarized in detail in a Technical Memorandum (BP-1) (PDF) and briefly listed here:
  • The optimal opening size is estimated to be approximately 90-feet as determined by hydrodynamic modeling procedures of the accepted MEP water quality model
  • Four alternative openings and bridge conceptual design were evaluated to replace the existing 50-foot span bridge and opening, and to extend an additional 40-feet to the east. From the evaluation, a two-span bridge was selected as the most practical and cost-effective at a total capital cost of $5,520,000.
  • The accepted MEP water quality model estimated the effective nitrogen removal of the new inlet to be 1,995 kg of nitrogen per year
  • The cost to remove this same nitrogen load through conventional wastewater nitrogen removal (sewering and advanced treatment) was estimated to be from $12,830,000 to $19,130,000 depending on the assumptions used. This indicated a significant saving compared to the $5 520-000-cost of the new bridge and opening. The new bridge and opening would be 43- to 29-percent of conventional wastewater nitrogen mitigation.

Next Steps

Based on these findings, the WQMC and Town have decided to proceed with the following next steps:
  • Advance this Demonstration Project independently of the CWMP Project.
  • Continue with permitting and design evaluations (Town Meeting appropriated these funds in Spring of 2013).
  • Submit a Notice of Project Change for this project to have it reviewed by MEPA.
  • Proceed with the many permits (local, regional, Commonwealth, and Federal) that would be needed once MEPA approval is obtained.
  • Evaluate the effects/benefits of inlet opening through monitoring and implementation.